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[en] The infrared spectral energy distributions of z ≳ 5 quasars can be reproduced by combining a low-metallicity galaxy template with a standard active galactic nucleus (AGN) template. The host galaxy is represented by Haro 11, a compact, moderately low metallicity, starbursting galaxy that shares typical features of high-z galaxies. For the vast majority of z ≳ 5 quasars, the AGN contribution is well modeled by a standard empirical template with the contamination of star formation in the infrared subtracted. Together, these two templates can separate the contributions from the host galaxy and the AGN even in the case of limited data points, given that this model has only two free parameters. Using this method, we reanalyze 69 z ≳ 5 quasars with extensive Herschel observations and derive their AGN luminosities [LAGN infrared luminosities from star formation [ and corresponding star formation rates (). The average infrared luminosity from star formation and the average total AGN luminosity of the z ≳ 5 quasar sample follow the correlation defined by quasars at z < 2.6. We assume that these quasar host galaxies maintain a constant average SFR (∼620 M⊙ yr−1) during their mass assembly and estimate the stellar mass that could form prior to z ∼ 5−6 to be Combining with the black hole (BH) mass measurements, this stellar mass is adequate to establish a BH–galaxy mass ratio at 0.1%–1%, consistent with the local relation.
[en] We present spectroscopy of the supernova remnant Cassiopeia A (Cas A) observed at infrared wavelengths from 10 to 40 μm with the Spitzer Space Telescope and at millimeter wavelengths in 12CO and 13CO J =2-1 (230 and 220 GHz) with the Heinrich Hertz Submillimeter Telescope. The IR spectra demonstrate high-velocity features toward a molecular cloud coincident with a region of bright radio continuum emission along the northern shock front of Cas A. The millimeter observations indicate that CO emission is broadened by a factor of two in some clouds toward Cas A, particularly to the south and west. We believe that these features trace interactions between the Cas A shock front and nearby molecular clouds. In addition, some of the molecular clouds that exhibit broadening in CO lie 1'-2' away from the furthest extent of the supernova remnant shock front. We propose that this material may be accelerated by ejecta with velocity significantly larger than the observed free-expansion velocity of the Cas A shock front. These observations may trace cloud interactions with fast-moving outflows such as the bipolar outflow along the southwest to northeast axis of the Cas A supernova remnant, as well as fast-moving knots seen emerging in other directions.
[en] We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 μm for 255 stars of types F4-K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the H-R diagram, to assign accurate stellar ages. Within this spectral type range, at 24 μm, 13.6% ± 2.8% of the stars younger than 1 Gyr have excesses at the 3σ level or more, whereas none of the older stars do, confirming previous work. At 70 μm, 22.5% ± 3.6% of the younger stars have excesses at ≥3σ significance, whereas only 4.7−2.2+3.7% of the older stars do. To characterize the far-infrared behavior of debris disks more robustly, we doubled the sample by including stars from the DEBRIS and DUNES surveys. For the F4-K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far-infrared excess with spectral type (detected fractions of 21.9−4.3+4.8%, late F; 16.5−3.3+3.9%, G; and 16.9−5.0+6.3%, early K). Taking this spectral type range together, there is a significant decline between 3 and 4.5 Gyr in the incidence of excesses, with fractional luminosities just under 10–5. There is an indication that the timescale for decay of infrared excesses varies roughly inversely with the fractional luminosity. This behavior is consistent with theoretical expectations for passive evolution. However, more excesses are detected around the oldest stars than are expected from passive evolution, suggesting that there is late-phase dynamical activity around these stars.
[en] A significant fraction of main sequence stars observed interferometrically in the near-infrared have slightly extended components that have been attributed to very hot dust. To match the spectrum appears to require the presence of large numbers of very small (<200 nm in radius) dust grains. However, particularly for the hotter stars, it has been unclear how such grains can be retained close to the star against radiation pressure force. We find that the expected weak stellar magnetic fields are sufficient to trap nm-sized dust grains in epicyclic orbits for a few weeks or longer, sufficient to account for the hot excess emission. Our models provide a natural explanation for the requirement that the hot excess dust grains be smaller than 200 nm. They also suggest that magnetic trapping is more effective for rapidly rotating stars, consistent with the average vsini measurements of stars with hot excesses being larger (at ∼2σ) than those for stars without such excesses
[en] To elucidate the intrinsic broadband infrared (IR) emission properties of active galactic nuclei (AGNs), we analyze the spectral energy distributions (SEDs) of 87 z ≲ 0.5 Palomar-Green (PG) quasars. While the Elvis AGN template with a moderate far-IR correction can reasonably match the SEDs of the AGN components in ∼60% of the sample (and is superior to alternatives such as that by Assef), it fails on two quasar populations: (1) hot-dust-deficient (HDD) quasars that show very weak emission thoroughly from the near-IR to the far-IR, and (2) warm-dust-deficient (WDD) quasars that have similar hot dust emission as normal quasars but are relatively faint in the mid- and far-IR. After building composite AGN templates for these dust-deficient quasars, we successfully fit the 0.3–500 μm SEDs of the PG sample with the appropriate AGN template, an infrared template of a star-forming galaxy, and a host galaxy stellar template. 20 HDD and 12 WDD quasars are identified from the SED decomposition, including seven ambiguous cases. Compared with normal quasars, the HDD quasars have AGNs with relatively low Eddington ratios and the fraction of WDD quasars increases with AGN luminosity. Moreover, both the HDD and WDD quasar populations show relatively stronger mid-IR silicate emission. Virtually identical SED properties are also found in some quasars from z = 0.5 to 6. We propose a conceptual model to demonstrate that the observed dust deficiency of quasars can result from a change of structures of the circumnuclear tori that can occur at any cosmic epoch.
[en] Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 μm, Hα, and UV down to rates of 0.03 M☉ yr–1. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 μm and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies
[en] The effects of dense environments on normal field galaxies are still up for debate despite much study since Abell published his catalog of nearby clusters in 1958. There are changes in color, morphology, and star formation properties when galaxies fall into groups and clusters, but the specifics of how and where these modifications occur are not fully understood. To look for answers, we focused on star-forming galaxies in A2255, an unrelaxed cluster thought to have recently experienced a merger with another cluster or large group. We used Hα, MIPS 24 μm, and WISE 22 μm to estimate total star formation rates (SFRs) and Sloan Digital Sky Survey photometry to find stellar masses (M *) for galaxies out to ∼5 r 200. We compared the star-forming cluster galaxies with the field SFR-mass distribution and found no enhancement or suppression of star formation in currently star-forming galaxies of high mass (log (M */M ☉) ≳ 10). This conclusion holds out to very large distances from the cluster center. However, the core (r proj < 3 Mpc) has a much lower fraction of star-forming galaxies than anywhere else in the cluster. These results indicate that for the mass range studied here, the majority of the star formation suppression occurs in the core on relatively short timescales, without any enhancement prior to entering the central region. If any significant enhancement or quenching of star formation occurs, it will be in galaxies of lower mass (log (M */M ☉) < 10).
[en] We present a sample of 290 24 μm-selected active galactic nuclei (AGNs) mostly at z ∼ 0.3–2.5, within 5.2 distributed as fields around each of 30 galaxy clusters in the Local Cluster Substructure Survey. The sample is nearly complete to 1 mJy at 24 μm, and has a rich multiwavelength set of ancillary data; 162 are detected by Herschel. We use spectral templates for AGNs, stellar populations, and infrared (IR) emission by star-forming galaxies to decompose the spectral energy distributions (SEDs) of these AGNs and their host galaxies, and estimate their star formation rates, AGN luminosities, and host galaxy stellar masses. The set of templates is relatively simple: a standard Type-1 quasar template; another for the photospheric output of the stellar population; and a far-infrared star-forming template. For the Type-2 AGN SEDs, we substitute templates including internal obscuration, and some Type-1 objects require a warm component ( K). The individually Herschel-detected Type-1 AGNs and a subset of 17 Type-2 AGNs typically have luminosities , and supermassive black holes of emitting at ∼10% of the Eddington rate. We find them in about twice the numbers of AGNs identified in SDSS data in the same fields, i.e., they represent typical high-luminosity AGNs, not an IR-selected minority. These AGNs and their host galaxies are studied further in an accompanying paper.
[en] We study the relation of active galactic nuclei (AGNs) to star formation in their host galaxies. Our sample includes 205 Type-1 and 85 Type-2 AGNs, 162 detected with Herschel, from fields surrounding 30 galaxy clusters in the Local Cluster Substructure Survey. The sample is identified by optical line widths and ratios after selection to be brighter than 1 mJy at 24 μm. We show that Type-2 AGN [O iii]λ5007 line fluxes at high z can be contaminated by their host galaxies with typical spectrograph entrance apertures (but our sample is not compromised in this way). We use spectral energy distribution (SED) templates to decompose the galaxy SEDs and estimate star formation rates (SFRs), AGN luminosities, and host galaxy stellar masses (described in an accompanying paper). The AGNs arise from massive black holes () accreting at ∼10% of the Eddington rate and residing in galaxies with stellar mass ; those detected with Herschel have IR luminosity from star formation in the range of . We find that (1) the specific SFRs in the host galaxies are generally consistent with those of normal star-forming (main sequence) galaxies; (2) there is a strong correlation between the luminosities from star formation and the AGN; and (3) the correlation may not result from a causal connection, but could arise because the black hole mass (and hence AGN Eddington luminosity) and star formation are both correlated with the galaxy mass.
[en] We present 24 μm photometry of the intermediate-age open cluster Praesepe. We assemble a catalog of 193 probable cluster members that are detected in optical databases, the Two Micron All Sky Survey (2MASS), and at 24 μm, within an area of ∼2.47 deg2. Mid-IR excesses indicating debris disks are found for one early-type and for three solar-type stars. Corrections for sampling statistics yield a 24 μm excess fraction (debris disk fraction) of 6.5% ± 4.1% for luminous and 1.9% ± 1.2% for solar-type stars. The incidence of excesses is in agreement with the decay trend of debris disks as a function of age observed for other cluster and field stars. The values also agree with those for older stars, indicating that debris generation in the zones that emit at 24 μm falls to the older 1-10 Gyr field star sample value by roughly 750 Myr. We discuss our results in the context of previous observations of excess fractions for early- and solar-type stars. We show that solar-type stars lose their debris disk 24 μm excesses on a shorter timescale than early-type stars. Simplistic Monte Carlo models suggest that, during the first Gyr of their evolution, up to 15%-30% of solar-type stars might undergo an orbital realignment of giant planets such as the one thought to have led to the Late Heavy Bombardment, if the length of the bombardment episode is similar to the one thought to have happened in our solar system. In the Appendix, we determine the cluster's parameters via bootstrap Monte Carlo isochrone fitting, yielding an age of 757 Myr (±36 Myr at 1σ confidence) and a distance of 179 pc (±2 pc at 1σ confidence), not allowing for systematic errors.